Effect of nitrate and glucose addition on denitrification and nitric oxide reductase (cnorB) gene abundance and mRNA levels in Pseudomonas mandelii inoculated into anoxic soil
The effect of glucose addition (0 and 500 μg C g−1 soil) and nitrate (NO3) addition (0, 10, 50 and 500 μg NO3–N g−1 soil) on nitric oxide reductase (cnorB) gene abundance and mRNA levels, and cumulative denitrification were quantified over 48 h in anoxic soils inoculated with Pseudomonas mandelii. Addition of glucose-C significantly increased cnorB p (P. mandelii and related species) mRNA levels and abundance compared with soil with no glucose added, averaged over time and NO3 addition treatments. Without glucose addition, cnorB p mRNA levels were higher when 500 μg NO3–N g−1 soil was added compared with other NO3 additions. In treatments with glucose added, addition of 50 μg NO3–N g−1 soil resulted in higher cnorB p mRNA levels than soil without NO3 but was not different from the 10 and 500 μg NO3–N g−1 treatments. cnorB p abundance in soils without glucose addition was significantly higher in soils with 500 μg NO3–N g−1 soil compared to lower N-treated soils. Conversely, addition of 500 μg NO3–N g−1 soil resulted in lower cnorB p abundance compared with soil without N-addition. Over 48 h, cumulative denitrification in soils with 500 μg glucose-C g−1 soil, and 50 or 500 μg NO3–N g−1 was higher than all other treatments. There was a positive correlation between cnorB p abundance and cumulative denitrification, but only in soils without glucose addition. Glucose-treated soils generally had higher cnorB p abundance and mRNA levels than soils without glucose added, however response of cnorB p abundance and mRNA levels to NO3 supply depended on carbon availability.
KeywordsDenitrification Gene expression Pseudomonas mandelii Nitric oxide reductase gene Organic carbon Soil
We are grateful to Drucie Janes for providing technical support. Funding for this project was supplied by an NSERC (Canada) Strategic Team Grant and an NSERC Discovery award to J.T.T. K. Shannon was a recipient of Ontario Graduate Scholarship. Infrastructure and equipment grants from the Canadian Foundation Innovation (CFI) and the Ontario Innovation Trust are sincerely acknowledged by J.T. Trevors.
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